Power supply for ionic vacuum device



Mai-ch 18, 1969 A. R. HAMILTON POWER SUPPLY FOR IONIC VACUUM DEVICE Filed June 15. 1967 ALLEN R. HAM/L TON I N VEN TOR.

United States Patent Office 3,433,550 Patented Mar. 18, 1969 9 Claims ABSTRACT OF THE DISCLOSURE A vacuum system comprising power supply means, power storage means, and switching means for selectively charging the power storage means from the power supply means and applying the power supply means and the charged storage means in a voltage-additive relationship to the ionic vacuum device to remove physical imperfections from electrodes thereof.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to vacuum systems and, more particularly, to systems including ionic vacuum devices having electrodes subject to the formation of physical imperfections thereon.

Description of the prior art Ionic vacuum devices are well known in the art and include ionic vacuum pumps and ionic vacuum gages having two or more electrodes adapted to be connected to high-voltage potentials. In the case of ionic vacuum pumps, gas molecules from the space to be evacuated are ionized by means of electrons, preferably with the assistance of a magnetic or electrostatic field, and the ionized gas molecules are entrapped on sorption surfaces and are preferably embedded thereon by means of sputtered material. In the case of ionic vacuum gages, gas molecules from the evacuated space subjected to measurement are also ionized by electrons and the ion current is measured to provide an indication of the degree of evacuation.

It has been known for some time that ionic vacuum devices are subject to the occurrence of field emission currents which impair their operation and which are due to the presence or formation of physical imperfections on electrodes of ionic'vacuum devices. These imperfections, which usually are of a sharp-edged or pointed configuration, promote local field enhancements giving rise to field emission currents.

The electrode imperfections here considered are of various origin. For instance, physical imperfections of the subject type are known to come about during the manufacture of the electrodes. Also, manufacturing imperfections which do not initially lead to objectionable field enhancement may build up during the operation of the ionic vacuum device until field emission currents appear. There also exists a tentative theory according to which whisker-like electrode protrusions form as a result of crystalline growth during the vacuum device operation. Observations on these phenomena are, for example, found in the article Field Enhancing Projections Produced by the Application of an Electric Field, by R. P. Little and S. T. Smith, Journal of Applied Physics, Vol. 36, pp. 1502-04 (April 1965).

Field emission currents are undesirable for several reasons. They obscure the true ion current, thereby defeating the usefulness of the device as an ionic vacuum gage or as a vacuum pump the ion current of which is measured to determine the degree of evacuation. They are responsible for the development of a considerable amount of undesirable heat. They tend to be erratic, thereby further interfering with the proper operation of the device. They impose an undesirable load on the power supply, which frequently results in a drop in supply voltage.

It has been recognized that objectionable electrode imperfections can be removed or that at least sharp points or edges thereof can be eliminated from time to time if the field emission currents are increased to a magnitude which causes material at these imperfections to melt or evaporate. This is accomplished by a temporary application of an enhanced high-voltage potential, which is considerably above maximum operating voltage, to the affected electrodes of the vacuum device.

According to the prior art, a separate high-voltage supply is provided for supplying the enhanced high voltage. Since this enhanced voltage is, as has been mentioned, considerably above the maximum operating voltage to which the vacuum device is subjected during pumping or vacuum measurements, the separate high-voltage supply is idle in the time intervals between the removal of the described imperfections. This leads to highly uneconomical conditions, since a removal of imperfections by application of the enhanced high voltage can be accomplished in a matter of some 1 to 5' minutes, while the tolerable intervals between necessary imperfection removals are generally of the order of days or weeks or, in rare instances, at least no longer than periods of several hours duration.

In addition, if a separate supply is used, the normal power supply has to be disconnected from, and the separate supply connected to, the vacuum device. After the imperfection removal process, the separate supply has to be disconnected from, and the normal power supply reconnected to, the vacuum device. This brings about the occurrence of longer periods of time during which no voltage is present on the electrodes of the vacuum device. Discontinuities of this type are known to have adverse efliects on ionic vacuum pumping and measuring processes.

In an effort to counter at least some of these incisive disadvantages, the use of a Tesla transformer arrangement for stepping up a normal operating voltage to the required enhanced high voltage has been proposed. This proposal has failed to materialize, since economically feasible Tesla transformer arrangements generally do not supply currents high enough to cause a satisfactory re moval of the type of imperfections described herein. Also, interruptions in the application of power to the vacuum device would still be present.

In a further effort to counter at least some of the problems mentioned above, one could contemplate the use of an additional secondary winding on the power transformer of the operating supply for the purpose of providing the desired enhanced high voltage. However, a brief reflection will show that this would not lead to a solution having the required amount of decisiveness as dictated by the extremely small fraction of the total operating time during which the enhanced high voltage is applied to the vacuum device. Just for the sake of a few minutes operation at a time, an additional high-voltage secondary winding would render the power transformer of the operating voltage supply bulkier and would intro-.

duce insulation problems.

SUMMARY OF THE INVENTION The invention overcomes the above mentioned disadvantages and provides an improved vacuum system comprising an ionic vacuum device, such as an ionic vacuum pump or vacuum gage, having electrodes subject to the formation of physical imperfections thereon, power supply means for providing the vacuum device with electrical operating power at at least one operating voltage, electrical storage means, such as at least one capacitor,

and switching means connected to the power supply means for selectively:

(1) Connecting the storage means to the power supply means to charge the storage means wtih the electrical power;

(2) Connecting the power supply means and the charged storage means in an at least partially voltageadditive relationship to the vacuum device to remove physical imperfections from electrodes of the vacuum device by an application of electrical power having a peak voltage higher than any peak operating voltage provided by the power supply means; and

(3) Disconnecting the storage means from the power supply means and from the vacuum device, and connecting the power supply means to the vacuum device to supply operating power to the vacuum device at an operating voltage which is lower than the higher peak voltage mentioned under (2) The system according to the invention obviates the need for the above mentioned additional power supply, Tesla transformer arrangement, or additional secondary winding, and permits a removal of electrode imperfections with the aid of simple power storage means and switches.

Unlike prior-art vacuum systems which employed capacitors as current limiting devices over the entire range of operation of an ionic vacuum pump, the system of the subject invention employs the named power storage means only during the removal of imperfections from electrodes of the vacuum device, and provides for a disconnection of these power storage means from the power supply means and the vacuum device during the operating cycles of the vacuum device between the im perfection-removal periods.

The system according to the invention permits the switching operations defined above to be effected speedily, so that there need not be longer periods of time during which the vacuum device is deprived of electrical potential at its electrodes.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing is a circuit diagram of an example of a power supply system in accordance with a preferred embodiment of the subject invention and also shows, in longitudinal section, an ionic vacuum pump connected to the illustrated power supply.

DESCRIPTION OF A PREFERRED EMBODIMENT The ionic vacuum pump shown in the accompanying drawing is of the triode type. This vacuum pump is of a conventional kind and has a housing 11 which defines a throat 12 that may be connected to a structure to be evacuated (not shown) with the aid of a flange 14. A cellular anode 16 and a pair of cellular sputtering electrodes 17 and 18 are located inside the pump housing 11. Inside areas of the pump housing 11 define collector surfaces or collector electrodes 20 and 21 in a conventional manner. A lead 23 extends through an insulating bushing 24 from an external anode terminal 25 to the anode structure 16. A further lead 28 extends through an insulating bushing 29 from an external sputter electrode terminal 30 to the sputter electrode structure 18. The other sputter electrode structure 17 is connected to the structure 18 by a lead 32. The means for mounting the electrodes 16, 17 and 18 are conventional and are thus not illustrated herein. The pump 10 further includes a magnet structure 34 which has two poles 35 and 36 for the provision of a magnetic field that penetrates the housing 11 and extends through the electrodes 16, 17 and 18.

A lead 38 finally connects the pump housing 11 and thus the collector surfaces 20 and 21 to a collector terminal 39. This terminal 39 is connected to another terminal 40 which, in turn, is interconnected with the anode terminal 25 through a current measuring device 41.

The operation of the illustrated pump 10 is also conventional and can be briefly summarized as follows.

A high voltage potential is applied between the terminals 30 and 40, with the terminal 30 b ing negatively biased and the terminal 40 receiving a positive bias. The magnitude of this high voltage potential is such that the negatively charged sputter electrodes 17 and 18 release electrons that collide with gas molecules situated inside the pump housing 11. The collision probability is increased by means of the magnetic field provided by the magnet structure 34 which causes electrons to move along helical paths. As is well known, these collisions cause the ionization of gas molecules which are subsequently trapped in the pump housing. Ions which impinge on the cell walls 43 of the electrodes 17 and 18 cause the sputtering of embedding material therefrom which assists the trapping of ionized gas molecules.

For explanatory purposes, a magnified housing section 11' and collector surface section 20 are shown within a circular outline 47. Several whiskers 50 are schematically illustrated within that outline as emerging from the collector surface 20'. It will be understood that physical surface discontinuities of the type of whiskers 50 or of similar imperfections may, during the operation of pump 10, not only form on the collector surfaces 20 and 21 but also on the electrode structures 16, 17 and 18. Wherever such formations may occur or be present during the operation of the pump, it is the purpose of the illustrated embodiment of the invention to enable a convenient and efiicient removal of such disturbances.

To illustrate this point, attention will now be devoted to the schematically illustrated power supply 60. This supply has a pair of input terminals 61 and 62 that are adapted to be connected to a conventional alternating current source or outlet. The illustrated power supply further includes a transformer 63 having a primary winding 64 and two secondary windings 65 and 66. The primary winding 64 is connected to the terminals 61 and 62 through a switch 68 which is closed when the operation of the power supply is desired. The above mentioned power storage means are present in the illustrated embodiment in the form of a capacitor 70 having one of its terminals connected to the secondary winding 66 through a lead 94. The above mentioned switching means include in the illustrated embodiment a rectifier cell 71 connected as shown to the capacitor 70 through a resistor 72. The function of these parts will be explained as the description proceeds.

The switching means further include a switch arrangement 74 composed of a number of ganged switches, including the switch 74a with stationary contacts 1a, 2a and 3a; switch 74b with stationary contacts 1b, 2b and 3b; switch 740 with stationary contacts 10, 2c and 3c; and switch 74d with stationary contacts 1d, 2d and 3d. The movable arms of switches 74a, 74b, 74c and 74d are, respectively, designated by the reference numerals 75a, 75b, 75c and 75d and are mechanically interconnected to be jointly actuable. The function of these switches will presently be described. For the moment, it will be noted that the illustrated power supply further includes a full wave rectifier 78 of a conventional construction having alternating current input terminals 79 and 80 and direct current output terminals 81 and 82, and having a filter capacitor 84 connected across these latter direct current terminals.

With the switch arrangement 74 in the illustrated position, the secondary windings 65 and 66 are connected in parallel with each other across the alternating current input terminals 79 and 80 of the full wave rectifier 78. More specifically, the upper end of the secondary winding 65 is connected to the rectifier input terminal 79 by a conductor 86. The lower end of the secondary winding 65 is connected to the rectifier input terminal 80 through a conductor 87, switch arm 75a, stationary switch contact In, conductor 88, and conductor 89. The upper end of the secondary winding 66 is connected to the rectifier input terminal 79 through a conductor 90, switch arm 75b, stationary contact 1b, conductor 92, and the above mentioned conductor 86. Finally, the lower end of the secondary winding 66 is connected to the rectifier input terminal 80 through the previously mentioned conductor 94, switch arm 75d, stationary contact 1d, conductor 95, conductor 96, and the above-mentioned conductor 89.

In the mode of operation just described, the currents, but not the voltages, of the secondary windings 65 and 66 are added to one another and are rectified by the bridge 78 to operate the pump at a voltage which is one-half the maximum operating voltage obtainable with a series connection of the secondary windings 65 and 66.

Series connection of the windings 65 and 66 is obtained by actuating the switch arrangement 74 to the position which is next to the one illustrated in the drawing. In that position, the upper end of the secondary winding 65 is again connected to the rectifier input terminal 79 in the manner described before, namely through the conductor 86. The lower end of the secondary winding 65 is connected to the upper end of the secondary winding 66 through the conductor 87, switch arm 75a, stationary contact 2a, conductor 98, and conductor 90. The lower end of the secondary winding 66 is connected to the rectifier input terminal 80 through the conductor 94, switch arm 75d, stationary contact 2d, conductor 96, and conductor 89. In this second position of the switch arrangement 74, the voltages of the secondary windings 65 and 66 are added to each other so that the pump 10 is operated at a voltage which corresponds to the maximum operating voltage provided by the supply 60.

In practice, it has been found that high continuous operating voltages encourage the formation of field emitters of the type shown at 50 in the circular outline 47, rather than to cause an elimination of these emitters. To remedy this situation, the above mentioned capacitor 70 and rectifier 71 are provided in accordance with the subject preferred embodiment of the invention.

When considering the function of these latter components, it will be noted that the secondary windings 65 and 66 are again connected in series when the switch arrangement 74 is in its third or lowermost position of the illustrated switch arrangement 74. More specifically, the lower end of the secondary winding 65 is connected to the upper end of the secondary winding 66 through conductor 87, switch arm 75a, stationary contact 3a, conductor 98, and conductor 90. At the same time, the previously existing connection of the lower end of secondary winding 66 to the rectifier terminal 80 is interrupted since the stationary contact 3d of the switch 74d is empty. Therefore, the lower end of the secondary winding 66 is connected to the rectifier input terminal 80 through the conductor 94, the capacitor 70, the resistor 72, a resistor 99, and the conductor 89. During alternate half cycles of the current through secondary winding 66, the capacitor 70, which acts as a power storage means, is charged with current from the secondary winding 66 through a circuit including conductor 90, a conductor 100, switch arm 75c, stationary contact 3c, rectifier cell 71, which acts as a unidirectional current conducting means, and resistor 72, as well as the previously mentioned conductor 94. The charge at capacitor 70 assumes a potential which is at least a fraction of the maximum peak operating voltage provided by transformer 63. In the illustrated embodiment, the charge at capacitor 70 assumes a potential which is similar to the voltage provided by secondary winding 66.

This capacitor charge potential is periodically added to the maximum peak operating voltage provided by the series-connected secondary windings 65 and 66. More specifically, during each half cycle in which the rectifier cell 7.1 is nonconducting, the capacitor 70 discharges itself in a circuit which includes the series-connected secondary windings 65 and 66 and which may be described as follows:

Rectifier input terminal 79, conductor 86, secondary winding 65, conductor 87, switch arm 75a, stationary contact 3a, conductor 98, conductor 90, secondary winding 66, conductor 94, capacitor 70, resistor 72, resistor 99, conductor 89, and rectifier input terminal 80.

Accordingly, the invention provides a power supply with which increased voltages for the purpose of the removal of electrode imperfections are applied at the flick of a switch with a minimum of auxiliary components. The necessity of interrupting the pumping process by changing external electrical connections is precluded and personnel can be familiarized with the operation of the power supply in a minimum of time. The simplicity of the subject apparatus also presents a safeguard against faulty circuit connections when the operation of the power supply is switched from one mode to another.

It will further be noted that the capacitor 70 is in the illustrated embodiment effectively disconnected from the system during the intervals between imperfection-removal operations by being bypassed by a circuit including the switch arm 75d, the stationary contact 1d and the lead 95, or the stationary contact 2d, as well as the lead 96. In this manner, the capacitor 70 is effectively discharged while being disconnected.

In addition, the provision and skillful utilization of two secondary windings according to the illustrated embodiment of the subject invention provides a power supply in which the three available voltages, namely the operating voltage during parallel connection of the secondary windings, the operating voltage during series connection of these windings, and the enhanced voltage provided during operation of the capacitor 70, can be dimensioned with respect to each other so as to provide for maximized results during the various modes of operation desired in practice. For example, the capacitor 70 can be dimensioned to have a capacity of from .10 to .20 microfarad. The windings 65 and 66 may be dimensioned to provide an operating voltage of some 3,000 to 4,000 volts when connected in parallel, and some 6,000 to 8,000 volts when connected in series. This results in a combined voltage close to or above the 10-kilovolt range when the capacitor 70 is active. In practice, heavy field emission currents due to significant electrode imperfection formations will initially drop the value of the combined voltage just mentioned. However, the magnitude of this voltage will rise as imperfections are melted or evaporated.

In view of the relatively broad scope of the subject invention, it is, of course, clear that the number of secondary windings may be limited to one, if only one magnitude of operating voltage is desired, while this number may be increased beyond two if more than two operating voltages are deemed necessary. Moreover, two or more capacitors can be utilized, depending on the voltage magnitudes desired. In that case, the capacitors are periodically charged and are periodically connected in series to combine the voltages of their charges. The provision of modifications of this kind is within the realm of those skilled in the art.

The same is obviously true with respect to other modifications within the scope and spirit of the subject invention.

I claim:

1. A vacuum system comprising:

(a) an ionic vacuum device having electrodes subject to the formation of physical imperfections thereon;

(b) power supply means for providing said ionic vacuum device with electrical operating power at at least one operating voltage;

(c) electrical power storage means; and

((1) switching means connecting to said power supply means for selectively (1) connecting said storage means to said power supply means to charge said storage means with electrical power;

(2) connecting said power supply means and said charged storage means in an at least partially voltage-additive relationship to said vacuum device to remove physical imperfections from electrodes of said vacuum device by an application of electrical power having a peak voltage higher than any peak operating voltage provided by said power supply means; and

(3) disconnecting said storage means from said power supply means and from said vacuum device, and connecting said power supply means to said vacuum device to supply said operating power to said vacuum device at an operating voltage which is lower than said higher peak voltage.

2. A vacuum system as claimed in claim 1, wherein said switching means are constructed and effective selectively to insert said storage means between said power supply means and said vacuum device in series to at least part of said power supply means.

3. A vacuum system as claimed in claim 1, wherein said switching means include at least one unidirectional current-conducting device and means for selectively connecting said unidirectional current-conducting device between said power supply means and said storage means to provide charging power for said storage means.

4. A vacuum system as claimed in claim 1, wherein said switching means include ganged switches connected to said power supply means.

5. A vacuum system as claimed in claim 1, wherein said storage means include at least one capacitor.

6. A vacuum system as claimed in claim 1, wherein said power supply means, said storage means and said switching means are integrated into one power unit.

7. A vacuum system comprising:

(a) an ionic vacuum device having electrodes subject to the formation of physical imperfections thereon;

(b) power supply means including at least two transformer secondary windings for providing said ionic vacuum device with electrical operating power at any of at least two operating voltages; and

(0) switching means connected to said power supply means for selectively (1) connecting said storage means to one of said secondary windings to charge said storage means with electrical power;

(2) connecting said secondary windings and said charged storage means in series to said vacuum device to remove physical imperfections from electrodes of said vacuum device by an application of electrical power having a peak voltage higher than any peak operating voltage provided by said secondary windings when connected in series; and

(3) electrically bypassing said storage means to permit said secondary windings to provide operating power for said vacuum device at operating voltages which are lower than said higher peak voltage.

8. A vacuum system as claimed in claim 7, wherein said switching means include a unidirectional currentconducting device, and selectively actuable means for connecting said unidirectional current-conducting device between one of said secondary windings and said storage means.

9. A vacuum system as claimed in claim 7, wherein said storage means include at least one capacitor.

References Cited UNITED STATES PATENTS 2,717,190 9/1955 Shoup 316-28 RICHARD H. EANES, JR., Primary Examiner. 

